This invention relates to an inter-frame coding circuit for a video signal.
It is known to use an inter-frame coding method for transmitting a video signal in order to reduce the quantity of transmitted information. The known inter-frame coding method produces a good compression factor for a video signal representing a picture containing little motion such as a still picture. But it is leff effective when a video signal containing a great deal of motion is processed. To overcome this drawback, a motion compensated inter-frame coding method has been described in which motion contained in the video signal is detected between frames and the video signal is coded by using the detected motion. One example of such a method is disclosed in U.S. Pat. No. 4,371,895 entitled, "CODED VIDEO SIGNAL TRANSMITTING AND RECEIVING SYSTEM". In the inter-frame coding method, when a channel error occurs in the transmitted data, the error decodes the picture reproduced therefrom. To cope with this problem, a refreshing operation in which a non coded video signal, which is not temporally correlated, is periodically transmitted. One example of an encoding, used for the refreshing operation, is a, so called previous value difference coding.
In the inter-frame coding method which uses motion compensation, an error, when occuring, spatially moves in the reproduced picture due to the motion compensation, which works to magnify the error. Therefore, it is frequently difficult to remove the error with the refreshing operation and, at worst, the error cannot be removed at all.